A Novel Technique Employing Tapered Fiber Bragg Grating to Solve the Axial/Transverse Forces Crosstalk in Microsurgical Instruments

This paper demonstrates the capability of retinal microsurgical instruments constructed with customized fiber Bragg gratings (FBGs) sensors to completely decouple the transverse and axial force components. In contrast to the constantly shifting Bragg wavelength, FBG bandwidth can only be tuned when a nonuniform strain/temperature distribution is applied. Using a tapered FBG (TFBG) at the neutral axis of the instrument makes the bandwidth tune-ability possible by applying forces both transversely and axially, while the bandwidth of the outer/lateral standard FBG (SFBG) due to the fiber symmetry remains insensitive to axial forces. Therefore, the crosstalk (transverse forces) in the TFBG can be easily filtered out when mixed forces are applied simultaneously. Tapered fiber mode analysis is carried out to calculate the local modes and is used in the analytic coupled-mode solution. Transfer-matrix method, then, is developed to analyze the reflected spectrum of the TFBG. We provide a developed mathematical model algorithm to show how force vectors can be measured. Tuning the reflected bandwidth is directly corresponding to the amount of the reflected optical power. Thus, the results show that the simulated needle sensors are able to measure transverse and axial forces with a sensitivity of 0.049 and 0.0026 dBm/mN, while the SFBG is insensitive to the axial forces. This novel method is applicable for microsurgical applications, i.e., vascular and cochlear implant surgeries and catheterization procedures.